1. Field of the Invention
The present invention relates to a sheet feeding device that is used in an image forming apparatus such as a printer, a copier, a facsimile, or a complex machine having a combination of these functions, as well as to an image forming apparatus having the sheet feeding device.
2. Description of the Related Art
In a conventional image forming apparatus such as a printer, a copier, or a facsimile, cut sheets of high quality paper, regular paper specified by a copier manufacturer, and so on are typically used as a sheet that can be fed continuously into the image formation apparatus.
In recent years, however, diversification of sheets has progressed to the point where not only sheets of high quality paper, regular paper, and so on having low surface smoothness are used. In particular, as colorization techniques become more advanced in image forming apparatuses, the use of enhanced-whiteness gloss coated paper having high surface smoothness (composite paper coated on one or both sides with a coating color, which is a type of paint, with the aim of improving printing suitability) is becoming more widespread. In other words, in recent years, there is a high demand for carrying not only high quality paper and regular paper, but also the coated paper described above, as well as film sheets, tracing paper, and so on using the same machine type. The volumes of coated paper, film sheets, tracing paper, and the like easily expand especially when they absorb moisture under a high-humidity environment. Hence, special measures must be taken in relation to sheet feeding (sheet dispatch).
Moreover, in recent years, with the demand for high speed sheet feeding, an image forming apparatus is used in which a pickup roller is constantly in contact with sheets even after completion of feeding the first sheet and when feeding of the next sheet is started.
However, when the pickup roller remains in contact with the sheets, the components contained in the pickup roller adhere to the sheets, causing a problem in which the surfaces of the sheets get contaminated. Further, when a sheet having high surface smoothness, such as gloss art paper or coat paper is used, adhesion of the components contained in the pickup roller damages the smoothness of the surface of the sheet. Moreover, a sheet with high surface smoothness easily swells when absorbing moisture, causing a problem in which wrinkles are easily generated on the sheet.